SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash, cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Restricted Cash
Cash and cash equivalents	$ 44,669	$ 114,573
Restricted cash - current	5,643	5,643
Restricted cash - noncurrent	315	315
Cash, cash equivalents and restricted cash	$ 50,627	$ 120,531	$ 161,201	$ 179,679

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalentsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant